In many medical diagnostic and therapeutic procedures, a physician or other trained clinician injects fluid into a patient. For example, during a computed tomography (CT) procedure, a physician may inject a contrast medium into a patient to help improve the visibility of internal bodily structures in one or more X-ray images that are taken during the procedure. To inject the contrast medium, the clinician may use a manual injection syringe, or may alternatively use a powered contrast media injection device. A cannula is coupled to the manual injection syringe or injection device and is used to inject the contrast medium into the patient (such as into a vessel in the patient's hand or arm).
Extravasation is often characterized as an accidental infusion of an injection fluid, such as a contrast medium, into tissue surrounding a blood vessel rather than into the blood vessel itself. Extravasation can be caused, for example, by a fragile vascular system, valve disease, inappropriate needle placement, or patient movement resulting in the infusing needle being pulled from the intended vessel or causing the needle to be pushed through the wall of the vessel. Furthermore, high injection pressures and/or rates of some modern procedures increase the risk of extravasation. In CT, for example, contrast injection flow rates can range, in some cases, from 0.1 to 10 ml/s, which may increase the potential for extravasation.
Complications related to extravasation may potentially be quite severe and may include tissue necrosis. This may require reconstructive surgery to repair. It is, therefore, very important when performing fluid injections to detect extravasation as soon as possible and discontinue the injection upon detection.
Several extravasation detection techniques are known in the art. Two simple and very useful techniques for detecting extravasation are palpation of the patient in the vicinity of the injection site and simple visual observation of the vicinity of the injection site by a clinician. In the palpation technique, the clinician manually senses swelling of tissue near the injection site resulting from extravasation. When using the visual observation technique, it is also sometimes possible to directly observe any swelling of the skin in the vicinity of an injection site resulting from extravasation.
In addition to the palpation and observation techniques, there are a number of automated methods of detecting extravasation. These methods include forms of subcutaneous temperature detection at or near the injection site, microwave extravasation detection, impedance change detection and measurement, optical sensing detection, as well as certain other techniques. Some of these methods provide for an automatic triggering of an alarm condition upon detection of extravasation.